As a technique to impart photosensitivity to a polyimide resin, there is, for example, a method of chemically bonding a crosslinkable group to a soluble polyimide precursor as disclosed in JP-A-54-116216 or JP-A-54-116217, or a method of mixing a crosslinkable monomer as disclosed in JP-A-54-145794 or JP-A-57-168942.
The above methods are of a negative type wherein an exposed portion is crosslinked and insolubilized by light, and they have a problem in safety, since an organic solvent is employed for the development, and swelling of the exposed portion by the developer will take place, whereby it will be difficult to carry out fine processing with high resolution.
Whereas, recently, a positive photosensitive resin material which can be developed by an alkali aqueous solution, has been developed and has attracted an attention. As such a photosensitive resin composition, a composition having an orthoquinone diazide compound mixed to an organic solvent-soluble polyimide resin having hydroxyl groups introduced (JP-A-64-60630) or a photosensitive resin composition with a high resolution having a polyimide orthoquinone diazide compound excellent in transparency incorporated (JP-A-3-209478) is known.
By such methods, it has been made possible to obtain a positive photosensitive polyimide resin which can be developed by an alkali aqueous solution and which is excellent in sensitivity and developability.
However, from the viewpoint of the surface water repellency characteristics, the coating film thereof will usually have a high surface energy, good wettability with water or an organic solvent, or with an ink containing a dye or pigment, and its contact angle will usually be low, since it contains phenolic hydroxyl groups, carboxyl groups, thiophenol groups, sulfonic groups, etc. in the polyimide resin.
On the other hand, display devices for various displays employing liquid crystal display elements or organic EL display elements, have found a remarkable development by virtue of the excellent characteristics such as small sizes, light weights, low power consumption, etc. Accordingly, in order to further improve the display quality, requirements for the components to be used have become increasingly severe. Among them, the technology for preparing a substrate for a full color display employing an ink jet system has been actively studied in recent years. For example, with respect to the preparation of a color filter in a liquid crystal display device, as opposed to the conventional printing, electrodeposition, dying or pigment-dispersing method, a color filter and a method for its production wherein preliminarily patterned partitions (hereinafter referred to as banks) for defining pixels, are formed of a light-shielding photosensitive resin layer, and ink droplets are dropped in openings defined by such banks, have been proposed (JP-A-10-206627, JP-A-11-326625, JP-A-2000-187111). Further, also with respect to an organic EL display device, a method has been proposed wherein banks are preliminarily prepared, and an ink to form a luminescent layer is likewise dropped to prepare an organic EL display device (JP-A-11-54270).
However, in a case where ink droplets are to be dropped to areas defined by banks by an ink jet method, it is necessary to let the substrate have an affinity to ink and to let the surface of banks have an ink repellency, in order to prevent overflow of ink droplets to adjacent pixels beyond banks.
To accomplish such an object, it is considered possible to let the substrate have an affinity to ink and to let the banks have an ink repellency by continuous plasma treatment, but such has a drawback that the process will be cumbersome. Further, there has been a case wherein a fluorinated polymer other than a fluorinated surfactant or polyimide, is incorporated to the photosensitive organic thin film, but such can hardly be regarded as practical because of many problems to be solved including not only the photosensitivity but also the coating properties such as the compatibility and the amount of incorporation.
The present invention has been made in view of the above-mentioned circumstances and it proposes to add a polyimide or a polyamic acid excellent in compatibility optionally and in a small amount to a positive photosensitive polyimide to provide a novel positive photosensitive resin composition which can be developed by an alkali aqueous solution and wherein the water repellency at the surface is improved and additional functions are imparted, while maintaining the excellent sensitivity and developability and the excellent characteristic such that the film reduction during the development or postbaking is less.